Making dimethyl sulfide from desugared spent sulfite pulping liquors



NOV. 24, n w MAKING DIMETH GOHEEN ET AL YL SULFIDE FROM DESUGARED LFITE PULPING LIQUORS SPENT SU Filed Dec. 6, 1957 D/METHYL SUL'F/DE YIELD DAVID W. GOHEE/V WILLIAM H. HEARD/V MERLE E. C/SNEY f 0 0 0 0 o 0 m 9 8 m 6 5 m 3 m m :55 vi SE51 meme: Q35? bfimm JAMES D. WETHERN INVENTORS BY *Z/ ATTORNEY.

United States Patent MAKING DIMETHYL SULFIDE FRGM DE- SUGARED SPENT SULFITE PULPlNG LIQ- UORS David W. Golieen, William M. Hearon, Merle E. Cisney, and James D. Wethern, all of Carnas, Wash, assiguors to Crown Zellerhach Corporation, San Francisco, Calif., a corporation of Nevada Application December 6, 1957, Serial No. 701,119

19 Claims. (Cl. 260-609) pulping liquors are set forth in Hagglund et al., U.S..

2,711,430 and Cisney et al. Serial No. 456,693, filed September 17, 1954, now US. 2,816,832, of which this application is a continuation in part. In these procedures the liquor is reacted with an inorganic sulfide or ele-' mental sulfur, respectively, for the conversion of the liquor constitutents to dimethyl sulfide, which then is distilled from the reaction mixture. While these procedures accomplish this conversion successfully when a spent liquor from alkaline pulping is used as a starting material, the "overall yields of dimethyl sulfide product are very low when sulfite spent liquor is employed.

Accordingly it is the general object of this invention to provide an improved process for making dimethyl sulfide from spent sulfite pulping liquor in much higher yields than have been attained heretofore. Italso is an important object of this invention to provide a process for making dimethyl sulfide inexpensively on a large commercial scale from spent sulfite pulping liquors which are available in large quantities at very low cost.

The manner in which the foregoing and other objects of this invention are accomplished will be apparent from the instant specification and claims considered together with the accompanying drawing consisting of a graph illustrating the effect of desugaring sulfite spent liquor on the yield of dimethyl sulfide obtainable by the presently described process.

The present invention is predicated on the discovery that a primary reason for the low yields of dimethyl sulfide product produced by the aforementioned procedures of Hagglund et a1. and Cisney et a1. resides in the fact that chemically reducing substances contained in spent sulfite liquors induce undesirable side reactions which reduce materially the final yield of dimethyl sulfide. Such reducing substances consist primarily of reducing sugars, other carbohydrates, and certain lignin sulfonic acids which have a reducing action as determined by the conventional Fehling test for reducing materials. They may be present in the amount of from 15-35% by weight, of the spent liquor solids.

Generally stated, therefore, the herein described process of making dimethyl sulfide comprises removing or degrading at least by weight of the content of chemically reducing substances from a spent sulfite waste liquor, insuring that the pH of the liquor from which the reducing substances have been removed lies above a 2,914,568 Patented Nov. 24, 1959 value of 7, and adding to the liquor from l-15% by weight, liquor solids basis, of an inorganic sulfur-bearing substance such as elemental sulfur. The resulting mixture then is heated to a temperature of from 180-500" C. for a time sufficient to form a substantial amount of dimethyl sulfide which thereafter is separated by distillation or otherwise.

The sulfide spent pulping liquor which is the starting material for the presently described process may be derived from the pulping of any of the conventional lignocellulose raw materials such as the coniferous species of trees, particularly hemlock, spruce, and white fir; the deciduous species of trees; and other plant materials such as straw, bagasse, etc. These materials in comminuted form are cooked with ammonium, sodium, calcium, or

' magnesium bisulfite under acid, neutral or alkaline condepending upon the amount of alkali used.

In a typical instance of the application of the acid sulfite procedure, the lignocellulose is cooked in digesters at l20-l55 C. and 65-125 p.s.i. for from 6 to 24 hours. The pressure then is reduced and the cellulose pulp product separated from the spent liquor.

The spent sulfite liquor which comprises the starting material for the present'invention comprises principally lignin in the form of salts of ligninsulfonic acids present in amount of from about 50-75% by weight, solids basis. In addition, there is present from about 15-35% by weight solids basis, of wood decomposition products having the common-property of reducing Fehlings solution. As noted above, these reducing materials comprise principally reducing sugars and other carbohydrates, together with certain lignin sulfonic acids having areducing action. It is these materials which must be substantially removed by the process of the present invention in order to secure a high yield of dimethyl sulfide.

Any one of several different procedures may be employed for the indicated purpose. In one such procedure, the spent liquor is steam stripped to remove free sulfur dioxide, cooled to F. and treated with certain nutrients as necessary to add missing essential elements and adjust the pH. These nutrients are commonly ammonium hydroxide, diammonium phosphate and potassium chloride. The liquor is fermented with Torula utilis, an organism which has been demonstrated to be the most satisfactory for the production of food yeast, or withother organisms having the common property of altering the reducing substances present in spent sulfite pulping liquor. The yeast is then removed from the liquor by centrifuging.

In another desugaring procedure, sulfite spent liquor is dialyzed to separate about 50% of the lignin sulfonic acids as non-dialyzable material. The dialyzable fraction then is further separated by passing it through two ion exchange columns, the first to deash it and the second to separate the sugars from the lignin sulfonic acids.

In a third desugaring process, the spent liquor is treated with lime to remove sulfur dioxide and the alkaline liquor is treated with air to oxidize various organic substances, i.e. sugars, which are present.

In a fourth such process lime is added to spent liquor first to precipitate calcium sulfite. Then a further quantity of lime is added to precipitate the lignin as basic calcium lignosulfonates which are separated from the sugars. by filtration and are then partially neutralized to form calcium lignosulfonates.

The desugared sulfite spent liquor remaining after the manufacture of ethyl alcohol therefrom by fermentation procedures, as: well: as the liquor remaining after: the: alkalineoxiilatioir process for-the: mamifacturezofivanillini also; are: suitable: as raw materials; for the; present: processt Thei modified spent liquors: resulting: from the; force going: procedures conventionally are termed; desugaredl spent: liquors and the procedures: by which they;v are: treated are conventionally termed desugaringai Hence;. the products and: processes are: thus: denominated: herein, although more; is: involved than a simple removal. of". the? sugarcontent: only ofthe. liquorss.

Asis indicated: the drawing,-. in order tor increase: materially the-.ultimateyield ofdimethyl; sulfideiobtainedti the desugaring operation: should be can-idi on. until: at least and preferably: at: least'.4D%-,.byweight\of the reducing substances have; been; separated: from the: lignin: sulfonict acids; on converted: to. non=reducing degradation products.

Since the solids: contentrof: the usual". desugaredi sulfite spent liquonis but 10-20%: by weight; ittisipreferred toz concentrateiteither before orsafter' desugariirg in:ordex to provide a liquor. having solids content of from 30-60% by weighti. Theiconcentration ofithezliquor m'ay" be eifectuated' in anysuitable" equipment such as con ventionalatmospheric or vacuum evaporators. If desired, the' concentrated; liquor then maybe further dehydrated by spray drying. to a; substantiallydry powder.

Where the liquor: does not. haverani inherent pH: of above7, preferably; of 11-14, it* may betreated with alkaline agents as required for pH: adjustment to the desired; level. Alkaline. agents;- suitable for: this use are the hydroxides, oxides. or ca'rbonatesofrthealkalimetals; the preferred agentbcing sodium hydroxide:- Any of these. agents; may be added; to: the: liquor with stirring until the selected pH=value=hasibeen attained.

After the spent. liquor? has been: subjected to: these preliminary; treatments-foridecreasingiitscontent of redllCJ- ing; substances, for adjustment of its solids content'and for adjustment of: its pH, it is mixed with a predetermined quantity of. an, inorganic. sulfur bearing substance suitable for conversion of the lignin'sulfonic acids: to reactiorr productsrincluding"dimethyl sulfide; Adiversityof inor ganicsulfur bearing-materials may be used for this pur pose, as long as they are: soluble: in aqueous alkaline-=- solutions and: possess the capacity to convert lignim methoxyl: to, dimethyl sulfide;. Examplesare elemental sulfur; the: water-soluble.sulfides,. e.g-; the alkali metal sulfides including, sodium sulfide: and. potassium sulfide; ammonium sulfide; hydrogen: sulfide; the water-soluble thiosulfates,- particularly sodium.thiosulfate; the Water-= 'tobenadded to; the spent liquoris somewhat variable,'-

depending upon ithernature and: identity: of i the substance? and of the spent liquor employed, sutficient-to furnisli from. 1-15 by weight sulfur; basedon the weight of the spent liquor solids; is generally suitable: 'Ihepreferred. amount is; sufiicient to; provide from 3'-l'0%- by weight-of sulfur, liquor'solids basis;

The .mixture of spent liquor and sulfur bearing-"mate rial is reacted in .a-rheated Tvesselawith Orv-without means-"- for agitating'itsrcontentsi Preferably, the vessel is' closed so that the: reaction may bercarridxout"under pressure! The. reaction iscarried-out underaconditions calculated to produce a maximum yieldr: ofdimethyl sulfidefin minimum time .withlminimum production of "undesirable byproducts; In general,- it should' be carried' out ata? temperaturezfrom- 180 500 C., preferably from 2005 300 C. The reaction time may vary from a period of. but a. few seconds at elevated temperature to one: ofa few hours at lower temperatures. In general, a time period of from 5-60 minutes is adequate when a temperature of from ZOO-300 C. is employed.

After the reacting materials have been maintained at the indicated temperature for theindicated time period, the vaporousproductmay be vented: into'acon'dense'r in a closed system. Thereupon the vapor is condensed to form a two-phase product comprising dimethyl sulfide and water. The upper or dimethyl sulfide layer then may be separated, dried and/or fractionally distilled to purify it. v

The process of the present invention is illustrated further by the following. examples-t Example 1 its content ofareducihgsubstrtnces had been reduced from.

anioriginal value of 21% to 4.7% by weight-gliquor solids basis; ize. until 78% of thereducing; substances had been removed.

The desugared liquor was concentrated to a: solids content of 44 .2%. Its pH then was adjusted from: an originalvalue of:16.8rt0- one 05915: Thereafter 25 grams of technical sodium sulfide (60% Na S) and 4.5 grams elemental: sulfuri were added to tlier'liquor, corresponded to a; sulfur usei of! 439% liquor. solids basis.- The? pH, after theadditi'on of the-sulfur bearing materials was: 1-3;.

Theresulting; mixture-1 was pla'cedc in: a' l lit'en stainless steel autoclave, heated to: a temperature of 240"" for 22 hours.- and maintained at this: temperature for ten minutes: Thereafter the; vapor's were vented from: the system: into a condenser with attached cooled receiving-I vessel. 5 The condensed product separated into-two layers:- Thev upper dimethyl sulfide: layer was decanted; dried over anhydrous sodium sulfate and filtered It was of good quality: and nwcighed 10.2 grams, representing a yield-of 4.-6%'diniethyl sulfide; solidsbasis. Therresidile imtheireacton was: fluid and .pumpable:

Example-'2 The resulting liquor was concentratedto' a solids; content of.46.5.%. and thereafter 25 grams-technical -sodium sulfide. (6Q.% Na S).-andr 4.5 grams'ielementalsulfur were. added... 'lihiszcorresponded to a-sulfur use of14.'6%,.solids basis. lhe pH: ofthe mixture" was adjusted to 13 by: the. addition of sodium hydroxide aften which ithe'mixture was .heatedto. 240 C. over'a periodofitwo hours; main-- tained at this. temperature .for'. 10-. minutes: and: distilled.

'Ili'eyieldofdimethylsu1fide=was:6 grams;.-corresp,ond+

ing;.to e216?!) yieldibased. on the liquor. solids. The:

residue in .thetreactor. W3S=fll1id1-and pumpable.

Example 3' Thisex'ample' illustrates the application of the present i process. to a spent liquor. containing a. relatively high amounfofredficir'ig,substances.

500* grams of' 473%; solids ammonium base-sulfite spentli'quor was, desug'ared inthe samev manner as in Example-1', de'cre'asir'rg' itscontent of reducing substances frorn'anoriginal' level oil 1% to. a level of 13.8% by weight, solids basis. This corresponds to a removal of 34.2% by weight of the reducing substances.

The desugared'mixture was alkalized with sodium hydroxide to a pH of 8.5, and 25 grams of sodium sulfide (60% Na s) and 4.5 grams sulfur added. The pH of the resulting mixture was 13.1 and the total amount of sulfur bearing substances present, calculated as elemental sulfur, was 4.5% by Weight, solids basis.

The mixture was heated to 240 C. and maintained at this temperature for 10 minutes after which it was distilled to give a yield of 3.5 grams of dimethyl sulfide. This corresponds to a yield of 1.5% by weight, based on the liquor solids. The residue in the reactor was a thick fluid but still pumpable.

Example 4 This example illustrates the application of the herein described procedure to the production of dimethyl sulfide from sulfite spent liquor which has been desugared by treatment with lime.

A 40% solids aqueous solution of calcium lignosulfonate was prepared from calcium base sulfite spent liquor by precipitation with lime, thereby separating the ligninsulfonates from all but about 4% of the reducing substances (80% removal) followed by neutralization with sulfuric acid to a pH of about 7. To 500 grams of the resulting solution there was added sufficient sodium hydroxide to adjust the alkalinity to a pH of 13.5. Thereafter 8.7 grams of elemental sulfur was mixed in, this corresponding to a use of 4.35% of sulfur, liquor solids basis.

The mixture was heated in a closed autoclave to 240 C. over a period of 90 minutes, maintained at this temperature for 10 minutes and distilled. The yield of dimethyl sulfide was 5.1 grams, or 2.6% based on the liquor solids. The residue in the autoclave was fluid and suitable for pumping.

Example 5 This example illustrates the application of the herein described procedure using an increased amount of added sulfur bearing material.

To 500 grams of the same pH 13.5 liquor as was employed in Example 4 was added 17.4 grams of elemental sulfur. This corresponds to a sulfur use of 8.7%, liquor solids basis. The mixture was heated in the manner set forth in Example 4. The condensed vapor yielded 9.2 grams (4.6% yield) of dimethyl sulfide. The residue in the autoclave was fluid and pumpable.

Example 6 This example illustrates the application of the herein described process to a calcium base sulfite spent liquor using a mixture of sodium sulfide and elemental sulfur as Example 7 This example illustrates the application of the presently described procedure to a spent liquor desugared by alkaline air oxidation.

Desugared sulfite spent liquor having a solids content of 45% was prepared by alkalizing ammonium base sulfite spent liquor with sodium hydroxide to a pH value of about 12, heating the mixture to a temperature of about 70 C. and passing air through the liquor until approximately 90% of its original content of reducing substances had been converted to non-reducing products. 500 grams of this desugared product was mixed with 25 grains of technical gradesodium sulfide (60% Na s), 4.5 grams elemental sulfur and sufi'icient sodium hydroxide to adjust the pH to 13.5. The total amount of sulfur bearing substances employed calculated as elemental sulfur was thus 4.75 liquor solids basis.

The mixture was heated a manner similar to that described in Example 4. The yield of dimethyl sulfide was 5.9 grams, or 2.6% liquor solids basis. The residue in the vessel was a thick, pumpable fluid.

Thus it will be apparent that by the present invention we have provided a process for making dimethyl sulfide which is effective in converting the constituents of sulfite spent liquor into a yield of dimethyl sulfide which is markedly higher than those obtained by the procedures of the prior art. Since appnoximately 2 million tons of sulfite spent liquor solids are produced annually in the United States, this improvement makes potentially available a vastly increased total quantity, of dimethyl sulfide for its various commercial applications.

The process is applicable furthermore, to liquors which have been desugared by any of the common procedures and thus makes use of a readily available, low cost starting material. Furthermorait maybe incorporated into the conventional sulfite pulp mill system for recovering various chemical products, or for manufacturing phenolic resins, tanning materials, dispersing agents, etc.

Having thus described our invention in preferred embodiments, we claim as new and desire to protect by Letters Patent:

1. A process of making dimethyl sulfide which comprises decreasing the content of chemically reducing substances in sulfite spent pulping liquor by at least 10% by weight, solids basis; insuring that the pH of the resulting liquor is above 7; adding to the resulting alkaline liquor from 1-15% by weight, based on the liquor solids, of sulfur in the form of an inorganic sulfur-bearing substance comprising at least one member of the group consisting of elemental sulfur and the water-soluble sulfides, thiosulfates, polysulfides and hydrosulfides; heating the mixture to a temperature of from 180500 C.; maintaining the mixture at 180-500 C. for a time sufiicient to form a substantial amount of dimethyl sulfide; and thereafter separating the dimethyl sulfide product from the mixture.

2. The process of claim 1 wherein the reducing substance content of the sulfite spent liquor is decreased by bacterial fermentation.

3. The process of claim 1 wherein the reducing substance content of the sulfite spent liquor is decreased by ion exchange and dialysis.

4. The process of claim 1 wherein the reducing substance content of the sulfite spent liquor is decreased by oxidation with oxygen containing gases in alkaline media.

5. The process of claim 1 wherein the reducing substance content of the sulfite spent liquor is decreased by 'lime precipitation of the ligninsulfonic acids contained in the liquor and separation of the resulting calcium lignosulfonates from the reducing substances.

6. The process of claim 1 wherein the sulfite spent liquor has a solids content of from 30-60% by weight.

7. The process of claim 1 wherein the reducing substance content of the liquor is decreased by at least 40% by weight.

8. The process of claim 1 wherein the pH of the liquor is 11-14.

9. The process of claim 1 wherein the amount of sulfur in the form of the inorganic sulfur-bearing substances is from 310% by weight, based on the liquor solids.

10. The process of claim 1 wherein the inorganic sulfur bearing substance comprises sodium sulfide.

11. The process of claim 1 wherein the inorganic sulfur bearing substance comprises elemental sulfur.

12. The process of claim 1 wherein the mixture is -7 heated. to andmaintained at a temperature betweeniOO" C. andT300 'C.

13. 'The process of dimethyl'sulfidewhichcomprises decreasing by at least.,l%1hy weig'htfthea'mount of chemically re'ducingrsubstances contained in .sulfite spent'i liquor, concentrating the resulting .desugared liquor to a solids content of from3O-60%'.b y wightflnsurihg that the pH of the resulting liquor isbetween ."11 audil i; adding to the'liquor 1fromI-31'0% "by weight,'base'd .on the' liguorsolids, ofsulfur in thefformof aninorganic sulfur bearing substance comprising at least one member of the group consistingofelemental sulfur and the watersoluble sulfides, thiosulfates, .polysulfides, and hyd'rosuh fides; heating the resulting mixture to a temperature of 200 300 C; the-mixture at ZOO-300 'C. fora time sufficient to Tform asubstanti'al amount of dimefthyl sulfide; and thereafter separating the dimethyl sulfidefrom the mixture.

14.The process of claiml3 wherein the inorganic sulfur bearing substance comprises sodium sulfide.

l'5.'The process of claim 13 wherein the inorganic suliiur bearing substance comprises elemental sulfur.

'16. Anprocess of making fdimethyl sulfide ,Which comprises providing desugared sulfite spent liguoffrorn which at least by weight of its content of reducing substances'has been removed,insuring1that the pH of the liquor-is above7, adding to the liquor from 1I'5'% by weight based on the liquor solids, or sulfur'in the form of aninorganic sulfur bearing substance comp'rising at least .onememberof the groupconSisting of elemental sulfur and the waterfsoluble' sulfides, thiosnliates, ,PQIY' sulfides and hydrostllfidesiheat'ing .the resultingmi iture to xa temperature sof flffrom 180 501)" "(3.; maintaining-the mixture at:I80500 1C. for a time sufiicient to fo'rmsa substantial amount of 'dimethylsulfide; .and thereeiter separating the dimethyl sulfide product. fnomllhe mixiure.

l7. The processof making dimethyl sulfidewllitih comprises provi'dingdesugare'd sulfitetspeut liquor from which at least 40% by weightof its content ofreducin'glsub- 's'tances'has' been removed and having a solidscontent ;of from about 30% to %".b y -weight, insuring 'thatthe pH of the liquor is between '11, and 14; adding to. the. liquor fr'om"3% to 10%by iweigh nibasedon thetliquorisolids, of sulfur in theform of an inorganic sulfur-beating substance comprising at least one member of the group consisting of elemental sulfur -andthe water-soluble sulfides, thiosulfates, spolysulfides, and hyrdosulfides; ,..heatirrg-1the resulting mixture ,toatemperature of, from 200-6 O O ,C., maintaining the mixture at ;200-.300; C. for a time sufficient to form a substantial amount of dimethyl sulfidezand thereafter separating the dimethyl sulfide :product from thevmixture.

.18. The ,processo f claim 17 wherein thezinorgauic sulfurrbear-ing substance comprises elemental sulfur.

19.iT-l1e .-process .of :claim 17 wherein the- -inorganic sulfurbearing substance comprises sodium sulfide.

Refer-encesfiited in the file of this patent L UNITED STATES PATENTS 3,711,430 Hagglund-et a1 June 21,4955 

1. A PROCESS OF MAKING DIMETHYL SULFIDE WHICH COMPRISES DECREASING THE CONTENT OF CHEMICALLY REDUCING SUBSTANCES IN SULFIDE SPENT PULPING LIQUIOR BY AT LEAST 10% BY WEIGHT, SOLID BASIS; INSURING THAT THE PH OF THE RESULTING LIQUIOR IS ABOVE 7; ADDING TO THE RESULTING ALKALINE, LIQUOR FROM 1-15% BY WEIGHT, BASED ON THE LIQUOR SOLIDS, OF SULFUR IN THE FORM OF AN INORGANIC SULFUR-BEARING SUBSTANCE COMPRISING AT LEAST ONE MEMBER OF THE GROUP CONSISTING OF ELEMENTAL SULFUR AND THE WATER-SOLUBLE SULFIDES, THIOSULFATES, POLYSULFIDES AND HYDROSULFIDES; HEATING THE MIXTURE TO A TEMPERATURE OF FROM 180-500* C., MAINTAINING THE MIXTURE AT 180-500* C, FOR A TIME SUFFICIENT TO FORM A SUBSTANTIAL AMOUNT AMOUNT OF DIMETHYL SULFIDE; AND 